Manual bisect info:
-----------------------
Good Build:56.0.2915.0
Bad Build:56.0.2916.0

This is regression issue broken in M-56

Deleted: Expected sync overlay.ogv 1.9 MB

	Expected sync overlay.ogv 1.9 MB View Download

Deleted: Actual sync ooverlay.ogv 2.0 MB

	Actual sync ooverlay.ogv 2.0 MB View Download

Using the per-revision bisect providing the bisect results,
Good build: 56.0.2915.0  (Revision:431137 ).
Bad build:  56.0.2916.0  (Revision:431463  ).

You are probably looking for a change made after 431282 (known good), but no later than 431283 (first known bad).
CHANGELOG URL:
The script might not always return single CL as suspect as some perf builds might get missing due to failure.
 
https://chromium.googlesource.com/chromium/src/+log/763c3fe382f8ae7c39cfa28191eab55b1036e4e6..0b510d0aebff97037598a470ff8f10901cc6187b 

From the CL above, assigning the issue to the concern owner

msarda@ Could you please look into the issue, pardon me if it has nothing to do with your changes and if possible please assign it to concern owner.

Review-Url: https://codereview.chromium.org/2484263002
     

Issue is reproduced on Mac 10.12.2 as well using beta 56.0.2924.76.

I am the right owner and we need to fix this as otherwise the user is blocked on this screen.

This is reproducible even in normal settings page and unable to scroll the sync page to proceed further with sign-in.

Note: Page Zoom need to set to in the Settings>Appearance>Page Zoom

Once the Sync modal is seen 
1) Unable to dismiss this using escape key.
2) Unable to work on any other tabs.
3) Only way to proceed further is to click Tab to navigate to the Ok/Cancel buttons.

Ligi@/Richard@/Mihai@: Added Releaseblock-Stable & Beta, feel free to modify if not appropriate.

Looks like the issue is reproducible only when page zoom is set to 125%.This was broken even before M56 branching, so not a blocker for today's release but definitely need a fix ASAP before next stable roll out.

Richard/ Mihai.. Please correct me if I am wrong.

I would not block beta either on this. The difference in M57 is that this dialog is not window-modal. So the user is blocked on this window if he/she cannot dismiss this dialog.

I think we need to detect this case and display the scrollbars in this case.

I agree, I don't think we should block today's releases as this has been in M56 for some time, but we should definitely get a fix.

Any updates?  We're planning on cutting the next stable on Monday 1/31.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/55529d0408f80b154fd394f4f8e1749f5d17329a

commit 55529d0408f80b154fd394f4f8e1749f5d17329a
Author: msarda <msarda@chromium.org>
Date: Sat Jan 28 00:28:46 2017

Fix layout of the sync and sign-in error dialogs when the page zoom is increased.

This CL does the following changes to the sync and sign-in error dialogs:
* Disables the web page zoom as these dialogs should look as native dialogs.
* Uses the document.body.offsetHeight instead of the scrollheight when computing
the preferred size for the dialog's webview as the scrollHeight is different
depending on the page zoom size (the values of the scrollHeight are equal to
offsetHeight / Chrome's page_zoom)
* Display the scrollbars as sometimes the dialog view may be smaller than the
preffered height of the scrollview.

BUG= 685021 
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2658783004
Cr-Commit-Position: refs/heads/master@{#446848}

[modify] https://crrev.com/55529d0408f80b154fd394f4f8e1749f5d17329a/chrome/browser/resources/signin/signin_error/signin_error.js
[modify] https://crrev.com/55529d0408f80b154fd394f4f8e1749f5d17329a/chrome/browser/resources/signin/signin_shared_css.html
[modify] https://crrev.com/55529d0408f80b154fd394f4f8e1749f5d17329a/chrome/browser/resources/signin/sync_confirmation/sync_confirmation.js

[Auto-generated comment by a script] We noticed that this issue is targeted for M-56; it appears the fix may have landed after branch point, meaning a merge might be required. Please confirm if a merge is required here - if so add Merge-Request-56 label, otherwise remove Merge-TBD label. Thanks.

This bug requires manual review: Only 0 days from stable, we might already have a stable candidate build
Please contact the milestone owner if you have questions.
Owners: amineer@(clank), cmasso@(bling), gkihumba@(cros), bustamante@(desktop)

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Thanks for the fix, we will verify in today's canary. 
If all looks good, please merge once its approved.

Seems like M57 merged is needed for this. If so, please request a merge to M57 by adding "Merge-Request-57" label. Thank you.

Your change meets the bar and is auto-approved for M57. Please go ahead and merge the CL to branch 2987 manually. Please contact milestone owner if you have questions.
Owners: amineer@(clank), cmasso@(bling), ketakid@(cros), govind@(desktop)

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Please merge your change to M57 branch 2987 ASAP (latest before 5:00 PM PT on Wednesday, 02/01/17) so we can pick it up for M57 Beta promotion release this week. Thank you.

Approving for merge into M56

Please merge your change to 2924 ASAP. We will be cutting the RC soon.

Per comment #24, this is already merged to M57 and M56 but we don't see merged Cls in this bug. Could you please point the merged CLs?

These were CLs I made this morning (with git drover):
https://codereview.chromium.org/2665113007/
https://codereview.chromium.org/2672433002/

Were they not added to the braches? What did I do wrong?

Note that I work from Paris (MTV+9 hours), so I cannot cherry-pick them until tomorrow.

Works fine in canary - 58.0.2999.0 (Official Build) (64-bit) but not in latest M56- 56.0.2924.87 and M57. The Cls are not merged on to either of the branches.

FYI: M56 stable is going out today.We can take the patch for any upcoming refreshes. So please get it merged on to M56 and M57 branches ASAP.

I used the instructions here https://www.chromium.org/developers/how-tos/drover to merge. Why did the merge not happen? I see both CL created by git drover as being commited.

Thanks for providing the Cls in #27.Now I see both on the branch, we will pick it up for upcoming releases.

Somehow bugdroid did update the bug.

The CLs were merged to M56 and M57:
https://chromium.googlesource.com/chromium/src.git/+log/refs/branch-heads/2924?n=1000
https://chromium.googlesource.com/chromium/src.git/+log/refs/branch-heads/2987?n=100

Please fix the bot that did not update this bug.

Correct, CLs were merged to M56 and M57.

Tested the issue on Win 10,Ubuntu 14.04 and Mac 10.12.2 on 57.0.2987.21 and 56.0.2924.88.
Scroll bar on the Sync-overlay is seen on Linux and Win but not on Mac.The Sync-overlay is visible completely without the scroll bars and out side the sign-in page.

msarda@:Please find the screen shot attached and let us know if its fine. 

Deleted: 685021_Feb_2_Mac.mp4 2.3 MB

	685021_Feb_2_Mac.mp4 2.3 MB View Download

Deleted: 685021_Feb_2_Win.mp4 3.6 MB

	685021_Feb_2_Win.mp4 3.6 MB View Download

On Windows, the dialog are small and thus display the scrollbars as they are bound to the size of the containing browser tab. Do you still see the scrollbars when tested on a larger screen (with a larger browser window) on Windows and Linux?

On larger screens with larger browser window I don't see the scroll bar on Windows and Linux. 

Note :  If we re-size the browser window after the singin dialog displayed in larger browser Window, Sign-in dialog doesn't get resized.

That is normal - we do not resize the dialog when the parent browser window is resized (this was the behavior of the dialog before this fix).